The longterm objectives of this proposal is to evaluate the safety of diagnostic ultrasound imaging in pregnancy. Although the benefits and advantages of diagnostic ultrasound are widely appreciated and accepted as a prenatal diagnostic tool it is not clear if diagnostic ultrasound usage during pregnancy is free of risk to the developing fetus. This concern is increased by the recent introduction of the pulse Doppler technique for prenatal diagnostic purposes. This technique is used in the third trimester of pregnancy and presents an ultrasound intensity (SPTA) 5 to 10 fold greater than traditional obstetrical CW Doppler. Because of its complexity of structure and function the CNS is recognized as especially susceptible to toxic insults during this later period of prenatal development. The specific aim of this proposal is to evaluate the effects of pulsed Doppler Ultrasound at intensities comparable to clinical use on third trimester fetal rats. Five treatment groups consisting of a cage control, a sham control and three separate ultrasound intensities will be used in the study design. Following parturition the pups from each treatment group will be evaluated by a behavioral test battery to assess: 1) pregnancy outcome, 2) physical growth and maturation, 3) reflex and motor development, 4) sensory function, 5) activity and reactivity levels, 6) learning and memory abilities, and 7) functioning in neuromotor systems. These studies will be conducted under GLP guidelines to assure the quality and integrity of the data under a framework suitable for acceptance to Federal Regulatory Agencies (FDA). The results from these studies will provide information on the bioeffects of ultrasound during pregnancy on postnatal development and enable reasonable estimates of bioeffects and risks of ultrasound on developing organism.